Vapor-grown carbon fibers combine the desirable characteristics of high thermal and electrical conductivity, high strength to weight ratio, non- catastrophic failure modes, high modulus, marked anisotropy and chemical resistance. They are a relatively new form of graphite fiber which hold great promise for application in reinforced composite materials for prosthetic devices and as microelectrodes for monitoring cell processes. The inherent anisotropy of the electronic conduction suggests their application in the neural sciences. The goal of this research is to tailor or "fine-tune" the electrical and thermal conductivity, the tensile strength and the modulus and the surface properties through various doping, coating and annealing procedures to allow for their application in prosthesis and as microelectrodes and biologically-suited electrical signal transmission and nerve models. We will attempt to perfect the annular structure of vapor-grown fibers to give a "closure", the lack of active surface edges. "Closure" is necessary for those applications in the human body that require chemical inertness. This is provided by the low reactivity of the 001 planes of graphite. This "closure" also enhances the resistance to oxidation by presenting a very low reactive-edge surface area. We propose to coat fibers via plasma deposition with diamond to lower porosity and increase the physical strength of the fibers. Alternatively, surface roughness will be incorporated into the fibers when growth into tendons and muscle fibers is desired. This process will be carried out through controlled oxidation. Through the use of solid-state ESR measurements, guided by our newly developed theoretical treatment, we will characterize vapor-grown carbon fibers for biological applications. The extremely important properties of electron mobility, conductivity anisotropy, crystallite size, degree of basal plane ordering,a nd electron diffusion constant will be inferred from analysis of ESR absorption lineshapes. Electron microscopy will reveal structural modifications due to changes in growth conditions and those accompanying thermal annealing. Measurement of total surface area with krypton and active surface area with oxygen will be performed. Oxygen surface concentration will be determined by monitoring the Ols and Cls XPS intensities. Surface order will be probed with low-energy electron diffraction. The utility of these fibers as microelectrodes will be studied in collaboration with Dr. Greg Swain at the Center for Bioanalytical Research at the University of Kansas. All of the above-mentioned properties of vapor-grown fibers depend critically upon the method of their thermal and chemical preparation. New growth methods will be employed in an effort to enhance the fibers' usefulness. We will, thus, determine the optimal preparation and processing conditions which will lead to advanced materials for prothesis, neural and biochemical use.